9.3 Process of Science Questions
1) Classification in Science: Usually, the first task of any science is to classify the available
observations. Often, the initial classification scheme reflects the historical order of discovery in
addition to nature itself. In this question, we will use our solar system as an example. Make a
complete list of all of the solar system components that you have studied in the last three
chapters. Then try to place this list in historical order of discovery. For example, start your list
with the Sun, Moon, Earth, and 5 “classical” planets, which have been known for all of human
history, and end your list with Eris. Can you see the historical order of discovery reflected in the
classification of objects on your list? Have there been occasions when this classification scheme
has been revised? Finally, does the classification scheme for the solar system introduce any
artificial divisions, making strict categories from objects with a continuous range of properties?
2) The Oort Cloud: The objects in the Oort Cloud are frozen “snowballs,” each a few kilometers
across and at distances of thousands of astronomical units from the sun. What do you think the
potential is to directly observe (via some sort of telescope) or directly visit (via a space mission)
an object in the Oort cloud? Do you think that the existence of this component of the solar
system is less well established than other components, such as the Kuiper Belt? What role does
the solar nebular theory for the formation of the solar system play in supporting the existence of
the Oort Cloud?
3) Can rocks fall from the sky? Many astronomers resisted the idea that rocks could fall from the
sky until undeniable eyewitness testimony was available. (The tide turned in 1803 when several
thousand stone fragments fell to the ground near L’Aigle, France, in the presence of hundreds of
witnesses.) Suppose that, for whatever reason, no meteorite falls could ever be witnessed. Would
it still be possible to make the scientific case that some rocks on the Earth had to have fallen
from interplanetary space? How would you make this case?
4) Visiting comets and asteroids: In recent years, several space probes have been sent to comets
and asteroids to physically interact with them. Briefly describe three of these missions, and
compare how each allows astronomers to better study the composition of these objects.
5) How would you search for Kuiper belt objects? What features would you include in a
systematic search for Kuiper belt objects — where in the sky would you look, and in which
wavelength regime? What features would you look for in images? What other types of objects
might you accidentally find, as well?
9.4 Short Answer Questions
1) Describe at least three ways in which our solar system would be different if orbital resonances
had never been important.
2) Describe some ways in which a meteorite can be distinguished from a terrestrial rock.
3) Describe the Deep Impact and Stardust missions and what they were designed to achieve.
4) Why is Pluto now considered to be a Kuiper-belt object?
5) Why is the Kuiper belt flat but the Oort cloud spherical?
6) What are “dwarf planets”?
7) Briefly describe the evidence suggesting that a large asteroid or comet hit Earth at the time of
the dinosaur extinction.
8) Briefly describe how an impact could lead to a mass extinction.
9) Suppose the planet Jupiter had never formed. How do you think the distribution of asteroids
and comets in our solar system would be different? Explain.
10) The mission New Horizons was the first to fly by Pluto and its moon. Describe some of the
major discoveries made by this mission.
11) Suppose the asteroid or comet that struck Earth 65 million years ago had instead missed us.
Describe how life on Earth today might be different.
12) What are the primary differences between the orbit of a Kuiper belt comet and that of an
Oort cloud comet?
13) Given the relatively small size of a comet or asteroid (compared to Earth), why do they do so
much damage when they strike our planet?
14) Do you think large impacts on Jupiter are relatively rare, common, or very common? Support
your answer.
15) Once a comet enters an orbit that carries it into the inner solar system, what is the inevitable
fate of this comet?
16) Why do we base the age of the solar system on the age of the primitive meteorites, and not
processed meteorites?
17) You are walking on a solid surface. The surface gravity is comfortable, but it is “hot, hot,
hot!” Your body is being squeezed in all directions due to the high pressure; it’s almost like being
deep in the ocean. Your life-support belt is corroding. The Sun, barely visible through the haze,
is near your meridian. You hope for nightfall (unaware that it would provide no relief), but you
already have been stuck on this planet for nearly 72 hours, and the Sun seems not to have moved
through the sky (and, if it moved at all, it moved eastward from the meridian).
18) It is very cold, but otherwise comfortable. You breathe deeply. Although there is no oxygen,
the air pressure is quite tolerable and seems almost Earth-like (because it is mostly nitrogen).
Your vista includes the breathtaking sights of an ocean of liquid methane and methane-snow-
capped mountains (although the atmosphere is very smoggy, and the visibility is limited). Your
solar day is about 16 Earth days long. A large, ringed object seems to hang in your sky, never
rising or setting; however, it does go through phases from new to full and back to new again with
the same 16-day period as the rising and setting of the Sun.
19) You find yourself in a maelstrom, whipped by incredibly high speed winds, which are rising
and falling in convective currents. On the rare occasions when you can assess your surroundings,
you notice a horizon that seems to go on “forever” (or, at least, much farther than the horizon on
Earth), and no solid surface anywhere. You get a glimpse of several large moons. The Sun races
through your sky, requiring only about 5 hours to rise nearly due east, cross the meridian at an
altitude of about 55° in the north, and then set due west.
20) You’ve been dropped at the edge of a cliff, looking down for what seems to be miles! In the
other direction the ground slopes up very gradually. The atmosphere is very thin even at the
mean surface level of this place. No matter, though, as you could not breathe this atmosphere
anyway because it is mostly carbon dioxide and contains no oxygen. You climb and climb. This
mountain must be three times the height of Mt. Everest and much broader at its base. There are
clouds around you, and you can find water ice as well. When you try to melt some ice, however,
it does not turn to liquid but sublimes to a gas.
21) You find yourself on a silent airless world! The lack of an atmosphere means that you must
be very careful not to let your skin burn from the Sun’s ultraviolet radiation. However, you are
able to determine that the Sun has about the same angular size that you are used to on Earth.
Although this world is clearly lifeless, you are surprised to find footprints and car tracks etched
in the powdery surface.
22) It’s cold. You are sitting on what appears to be a water ice-covered world. The Sun is low on
the horizon and circles the horizon once every 24 hours. Despite the low Sun, you can almost
“feel” the Sun’s ultraviolet radiation on your exposed face because there is little ozone to protect
you. Despite these discomforts, you are pleased to find that the air is quite satisfactory; oxygen
seems plentiful and you are able to breathe even without the life-support belt.
9.5 Mastering Astronomy Reading Quiz
1) Which of the following statements is not true?
A) Objects in the Kuiper belt are made mostly of rock and metal.
B) Objects in the asteroid belt are made mostly of rock and metal.
C) Objects in the Oort cloud contain large proportions of ice.
D) Objects in the asteroid belt and Kuiper belt orbit the Sun in nearly the same plane as the
planets, but objects in the Oort cloud do not.
2) A rock found on Earth that came from space is called ________.
A) a meteorite
B) a meteor
C) an asteroid
D) an impact
3) The asteroid belt is located ________.
A) between the orbits of Mars and Jupiter
B) between the orbits of Earth and Mars
C) between the orbits of Jupiter and Saturn
D) beyond the orbit of Neptune
4) Which statement about asteroids is not true?
A) If we could put all the asteroids together, they would make an object about the size of Earth.
B) Many, but not all, orbit the Sun in the asteroid belt.
C) Some are more like loosely bound piles of rubble than solid chunks of rock.
D) Most asteroids are not spherical in shape.
5) A typical meteor is created by a particle about the size of a ________ or smaller.
A) pea
B) baseball
C) car
D) basketball
6) What do we mean by a primitive meteorite?
A) a piece of rock that is essentially unchanged since it first condensed and accreted in the solar
nebula some 4.6 billion years ago
B) a meteorite that has undergone some remelting
C) a type of meteorite that is usually made mostly of high-density metals
D) a meteorite that fell to Earth at least 4 billion years ago
7) Among discovered meteorites, we have found some with all the following origins except
________.
A) Comet Halley
B) the surface of Mars
C) the surface of the Moon
D) a shattered asteroid
8) Which statement is not true of all comets in our solar system?
A) Comets always have tails.
B) All comets are icy in composition.
C) All comets orbit the Sun.
D) All comets are leftover planetesimals that originally condensed beyond the frost line in the
solar nebula.
9) Which direction does a comet’s plasma tail point?
A) straight away from the Sun
B) straight behind the comet in its orbit
C) perpendicular to the ecliptic plane
D) always almost due north
10) When a comet passes near the Sun, part of it takes on the appearance of a large, fuzzy ball
from which the tail extends. This part is called ________.
A) the coma
B) the nucleus
C) the plasma tail
D) the Oort core
11) The total number of comets orbiting the Sun is estimated to be about ________.
A) 1 trillion
B) 1,000
C) 100,000
D) 1 million
12) Photographs sent back from the recent New Horizons mission showed Pluto’s moon Charon
to
A) have smooth plains resulting from recent geological activity.
B) have a very old surface, indicating no geological activity.
C) be composed primarily of rock.
D) show signs of erosion.
13) According to current evidence, Pluto is best explained as ________.
A) a large member of the Kuiper belt
B) a terrestrial planet that is surprisingly far from the Sun
C) a very small jovian planet
D) an escaped moon of Neptune
14) Why was the discovery of Eris significant in the debate over how to classify Pluto?
A) Eris is about the same size and slightly more massive than Pluto, so if Pluto is considered to
be a planet, then Eris should be too.
B) Eris is made mostly of rock and metal, so it should replace Pluto as the true ninth planet.
C) Eris has a very different composition than Pluto, so Eris should be classified differently.
D) Eris is actually an extrasolar planet ejected by another solar system, so Pluto might be too.
15) What was the Shoemaker-Levy 9 impact?
A) the 1994 impact of a chain of comet fragments into Jupiter
B) the impact thought to have wiped out the dinosaurs
C) the impact that created the Moon’s largest crater
D) the ninth impact witnessed by astronomers in modern times
16) What do we mean by a mass extinction?
A) the extinction of a large fraction of the world’s plant and animal species in a relatively short
period of time
B) the extinction of large animals, such as dinosaurs
C) an extinction caused by the impact of an asteroid or comet
D) the extinction of any species of plant or animal that has mass
17) If the hypothesis tracing the extinction of the dinosaurs to an impact is correct, the dinosaurs
died off largely because ________.
A) of global climate effects initiated by dust and smoke that entered the atmosphere after the
impact
B) of injuries suffered from direct hits of pieces of the asteroid or comet
C) the ensuing fireball that burned most of Earth’s surface
D) the impact caused massive earthquakes worldwide
9.6 Mastering Astronomy Concept Quiz
1) Why is the asteroid Ceres now considered to be a dwarf planet?
A) It is large enough to be round.
B) It is made mostly of rock.
C) It is larger than Pluto.
D) It orbits inside the frost line.
2) If we could put all the asteroids together, their total mass would be ________.
A) much less than the mass of any terrestrial planet
B) about the mass of Mercury
C) about the mass of Earth
D) greater than the mass of Earth but less than the mass of Jupiter
3) Why didn’t a planet form where the asteroid belt is now located?
A) Gravitational tugs from Jupiter prevented material from collecting together to form a planet.
B) There was not enough material in this part of the solar nebula to form a planet.
C) There was too much rocky material to form a terrestrial planet, but not enough gaseous
material to form a jovian planet.
D) The temperature in this portion of the solar nebula was just right to prevent rock from sticking
together.
4) Gaps in the asteroid belt (often called Kirkwood gaps) are caused by ________.
A) orbital resonances with Jupiter
B) tidal forces from the Sun
C) tidal forces from Jupiter
D) the competing gravitational tugs of Mars and Jupiter
5) When you see the bright flash of a meteor, what are you actually seeing?
A) the glow from the surrounding air as a small particle burns up in our atmosphere
B) emission of visible light from a particle that has not yet entered Earth’s atmosphere
C) a star that has suddenly shot across the sky
D) the flash that occurs when a speeding rock from space hits the ground
6) In science fiction movies, spaceships are often shown dodging through large numbers of
closely spaced, boulder-size objects. Which of the following real things in our solar system
would look most like such science fiction dangers?
A) the rings of Saturn
B) the asteroid belt
C) the atmosphere of Jupiter
D) the Oort cloud
7) Suppose you find a meteorite made almost entirely of metal. Which of the following
statements must be true?
A) Your meteorite is a fragment from the core of a large asteroid that shattered in a collision.
B) Radiometric dating will show the age of your meteorite to date to the formation of our solar
system.
C) Your meteorite was blasted off the surface of Mars by an impact.
D) Your meteorite is a fragment of an object from the Kuiper belt.
8) Which of the following objects are probably not located in the same general region of the
solar system in which they originally formed?
A) Oort cloud comets
B) Kuiper belt comets
C) asteroids of the asteroid belt
D) Pluto
9) Suppose there were no solar wind. How would the appearance of a comet in our inner solar
system be different?
A) It would have only one tail instead of two.
B) It would not have a coma.
C) It would not have a nucleus.
D) It would be much brighter in appearance.
10) Suppose we discover a new comet on an orbit that brings it closer to the Sun than Mercury
every 125 years. What can we conclude?
A) It has been in its current orbit for only a very short time compared to the age of our solar
system.
B) It came from the Oort cloud.
C) It came from the Kuiper belt.
D) It has a coma and tail during most of each orbit.
11) When we see a meteor shower, it means that ________.
A) Earth is crossing the orbit of a comet
B) the solar wind is unusually strong
C) an Earth-approaching asteroid has recently come very close to our planet
D) meteor dust is causing rain drops to condense in our atmosphere
12) Why won’t Pluto collide with Neptune?
A) Pluto orbits the Sun exactly two times for every three Neptune orbits, which ensures they
never come close together.
B) Pluto is always much farther from the Sun than Neptune.
C) Pluto’s orbit never comes anywhere close to Neptune’s orbit.
D) Pluto is a lost moon of Neptune.
13) What is Pluto’s moon Charon thought to have in common with our own Moon?
A) It probably formed as a result of a giant impact.
B) It has the same basic composition.
C) It has the same approximate mass.
D) It has the same average density.
14) Which of the following supports the idea that Pluto is like a large comet in the Kuiper belt?
A) Pluto’s composition appears to match that of other known Kuiper belt comets.
B) Pluto grows a coma and a long tail at its closest approach to the Sun.
C) Pluto probably originated in the Oort cloud.
D) Pluto’s has numerous moons.
E) Pluto is not the largest object in the Kuiper belt.
15) The discovery of Eris ________.
A) was not surprising, because other Kuiper belt objects approaching the size of Pluto had
already been discovered
B) was surprising, since we thought we knew about all large objects in the solar system
C) was surprising, due to its “backwards” orbit around the Sun
D) was not surprising, because the existence of a massive “Planet X” had been predicted nearly a
century ago
16) Which of the following is not a piece of evidence supporting the idea that an impact caused
the mass extinction that occurred 65 million years ago?
A) Fossilized dinosaur bones contain fragments of rock from the impact.
B) Unusually large abundances of iridium and other rare metals are found in a layer of clay that
dates to 65 million years ago.
C) A large, buried impact crater found along the coast of Mexico dates to 65 million years ago.
D) Grains of quartz formed under high pressure are found in a layer of clay that dates to 65
million years ago.
17) Suppose that large jovian planets had never formed in our solar system. Which of the
following would most likely be true?
A) Neither the asteroid belt nor Oort cloud would exist.
B) Earth would have suffered far fewer impacts.
C) There would be a large empty region in our solar system between the orbit of Mars and the
Kuiper belt.
D) Earth would orbit much closer to the Sun.